Device and method for reading out information stored in a storage layer, and x-ray cartridge

ABSTRACT

A device and a method for reading out information stored in a storage layer ( 15 ), and an X-ray cassette are proposed which make use for the purpose of erasing information stored in the storage layer ( 15 ) of an erasing means ( 11, 12, 14 ) which generates an erasure radiation ( 17 ). This erasure radiation ( 17 ) can have both a first and a second intensity, the first intensity being larger than the second intensity.

FIELD OF THE INVENTION

[0001] The present invention relates to a device and a method forreading out information stored in a storage layer, and to an X-raycassette.

BACKGROUND OF THE INVENTION

[0002] Particularly for medical purposes, an image which is stored in astorage layer as a latent image is produced from an object, for examplea patient, by means of X-ray radiation. It is mostly a phosphor layerwhich is used as the storage layer in this case. The storage layer isexcited by means of a radiation source in order to read out the X-rayimage stored in the storage layer. Therefore, on the basis of thisexcitation the storage layer emits light which has an intensitycorresponding to the stored X-ray image. The light emitted by thestorage layer is received by a receiving means and subsequentlyconverted into electric signals such that the X-ray image stored in thestorage layer can subsequently be visualized. The X-ray image can bedisplayed, for example, directly on a monitor, or else be written onto aphotographic X-ray film which can be used specifically for X-ray images.After the X-ray image has been read out from the storage layer, thelatter is erased by an erasing device, in order to be able to store asubsequent X-ray image.

[0003] Such storage layers can be arranged in an X-ray cassette.European patent EP 0 288 014 B1 discloses erasing a storage layer whichis located in an X-ray cassette. The X-ray cassette contains an openingmechanism such that the X-ray cassette can be opened in order to eraseinformation stored in the storage layer. Present outside the X-raycassette is an erasing means which outputs an erasure radiation. Thiserasure radiation is irradiated into the open X-ray cassette andprojected onto the storage layer. The irradiation of the storage layerby means of the erasure radiation erases the information stored in thestorage layer. The known X-ray cassette contains a reflector or adiffusing means for the purpose of reflecting the erasure radiationirradiated into the cassette, and of scattering it over the width of thestorage layer.

[0004] A device for reading out information stored in a storage layer isdisclosed in patent U.S. Pat. No. 5,038,037. An X-ray table for X-rayingpatients is described therein. The X-ray table contains two phosphorlayers which are fitted on the top side and underside of a tape andserve for storing X-ray information. Both for the phosphor layer fittedon the top side and for that fitted on the underside of the tape, theknown X-ray table has a dedicated device for reading out informationfrom this phosphor layer. Furthermore, the X-ray table contains twoerasing means which are used to erase the phosphor layers. A dedicatederasing means is provided for each of the phosphor layers. Serving aserasing means is an erasing lamp which—viewed in the transport directionof the tape—is arranged upstream of that point at which the X-ray imageof the patient is taken. As a result, an “old” X-ray image stored in thephosphor layer is erased before a “new” X-ray image is taken. Aplurality of erasing lamps arranged next to one another are likewiseused as erasing means, being arranged in the X-ray table below thatposition at which the X-ray image is projected onto the stationary tapewith the phosphor layers. Before the taping of a “new” X-ray image, the“old” X-ray image is therefore firstly erased with the aid of thiserasing means, the tape being stationary. In this type of erasing means,the phosphor layer cannot be used directly for a “new” picture. Theerasure of the phosphor layers does not take place until immediatelybefore the subsequent taking of a “new” X-ray image. This means thattime is lost and tuning takes place between the operations of erasureand subsequent storage. The erasure must firstly be terminated beforethe next X-ray image can begin to be taken.

[0005] Patent application WO 99/28765 discloses an X-ray cassette inwhich both a device for reading out information stored in the storagelayer and an erasing means for erasing information stored in the storagelayer are present. The erasing lamp extends over the entire width of thestorage layer in which information can be stored. By means of a drive,the erasing means is guided over the storage layer along a transportdirection running perpendicular to the line direction. The storage layercan be erased in this way line by line.

SUMMARY OF THE INVENTION

[0006] It is the object of the present invention to permit in a simpleand effective way erasure of information stored in a storage layer, anda high quality of reproduction of stored information.

[0007] It is possible on the basis of the configuration according to theinvention to avoid, or at least reduce, the occurrence of ghosts in thestorage layer. Such ghosts can occur when the device according to theinvention or the X-ray cassette is exposed to the scattered radiation ofother X-ray machines which can be located, for example, in the vicinity.Such scattered radiations can certainly be very slight individually, butthe addition of scattered radiations from a plurality of X-ray images ofother X-ray machines can nevertheless accumulate to form visible ghostsin the storage layer. Moreover, conventional storage layers can containsmall quantities of radioactive isotopes such as ²²⁶Ra, which likewiseemit slight amounts of radiation. These are further supplemented bynatural, cosmic radiations. Particularly in the case of lengthy non-useof the storage layer, these radiations can contribute to the occurrenceof the ghosts. Ghosts have a deleterious effect on the quality of thereproduction of the information read out. Ghosts can become noticeableas noise when stored information is read out. It is advantageouslypossible, moreover, to ensure on the basis of the invention that storageof “new” information is possible without the need to undertake priorerasure immediately before storage. There is no need to tune the erasingoperating to the storage operation.

[0008] The erasing means advantageously outputs an erasure radiation ofa larger, first intensity immediately after information of an image hasbeen read out from the storage layer. This ensures that the storagelayer is ready very quickly to take a new image after the storage of animage.

[0009] In a further advantageous refinement of the invention, theerasure radiation of a second, weaker intensity is output after theerasure radiation of the first intensity has been output. This preventsan undesired storage of scattered radiation striking the storage layer,since this scattered radiation is erased continuously by the erasureradiation.

[0010] In a particularly advantageous refinement, the erasure radiationis output onto the storage layer between the reading out of theinformation of a first image and the subsequent storage of informationof a second image. Storage of scattered radiation and the occurrence ofghosts during the entire time between the reading out of the first imageand the storage of the information of the second image are thereforeavoided. The quality of the reproduction of the information is furtherimproved thereby. Furthermore, the erasure radiation of the secondintensity can be output independently of the storage of information of anew image. Tuning between the storage and the erasure with the secondintensity is not required for the sake of simplicity.

[0011] It is preferable for there to be present a detection means fordetecting that radiation with the aid of which information is stored inthe storage layer. Consequently the erasing means can be switched offautomatically when storage of information of a new image begins. For thesake of simplicity, the detection means can contain a photodiodeupstream of which there is fitted a conversion layer for converting thestorage radiation into a radiation that has a wavelength which can bedetected by the photodiode.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] An exemplary embodiment will be described in more detail belowwith reference to the appended drawings, in which:

[0013]FIG. 1 shows a first exemplary embodiment of an X-ray cassetteaccording to the invention, with an erasing source of planarconfiguration,

[0014]FIG. 2 shows a sectional illustration of the first exemplaryembodiment of the X-ray cassette in accordance with FIG. 1,

[0015]FIG. 3 shows a second exemplary embodiment of an X-ray cassetteaccording to the invention with an erasing source fitted laterally atthe edge of the X-ray cassette,

[0016]FIG. 4 shows a sectional illustration of the second exemplaryembodiment of the X-ray cassette in accordance with FIG. 3,

[0017]FIG. 5 shows an example of an X-ray table in which a thirdexemplary embodiment of an X-ray cassette according to the invention isarranged, and

[0018]FIG. 6 shows a detailed schematic illustration of the thirdexemplary embodiment of the X-ray cassette with an exemplary embodimentof a reading head according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0019]FIG. 1 shows the first exemplary embodiment of an X-ray cassette 1according to the invention. This X-ray cassette contains a storage layer15. The storage layer 15 is a phosphor plate. X-ray images can be storedin the phosphor plate 15. The X-ray cassette 1 has a reading head 10 forreading out the X-ray images stored in the phosphor plate 15. Fittedalong the longitudinal sides of the phosphor plate 15 are two guide bars16 and 17 which serve for transporting and guiding the reading head 10.The reading head 10 can be transported by means of a drive (notillustrated) along the guide bars 16 and 17 over the surface of thephosphor plate 15 in a feed direction A. An erasing lamp 11 is locatedbehind the reading head 10. The erasing lamp 11 is connected to thereading head 10 and can, just like the reading head 10, be transportedby means of the drive (not illustrated) along the guide bars 16 and 17over the surface of the phosphor plate 15 in the feed direction A. Theerasing lamp 11 serves to erase information stored in the phosphor platewhich is still stored in the phosphor plate 15 after an X-ray image hasbeen read out by means of the reading head 10. During operation, theerasing lamp 11 emits an erasure radiation of a first intensity. Thisfirst intensity is advantageously so great that a single to and fromovement of the erasing lamp 11 over the phosphor plate 15 along thedirection A erases residual information, remaining in the phosphor plate15, of the X-ray image. After the phosphor plate 15 has been erased bymeans of the erasing lamp 11, the X-ray cassette is ready for taking asubsequent, second X-ray image. The erasing lamp 11 and the reading lamp10 extend in a line direction B over the entire width of the phosphorplate 15. The line direction B is perpendicular to the feed direction A.

[0020] A second erasing lamp 12 is arranged inside the X-ray cassette 1below the phosphor plate 15. This second erasing lamp 12 is of planarconfiguration. The surface of the second erasing lamp 12 runs parallelto that of the phosphor plate 15. The extent of the surface of thesecond erasing lamp 12 corresponds essentially to that of the phosphorplate 15 in which X-ray images are stored. The erasure radiation emittedby the second erasing lamp 12 has a wavelength that lies within thatwavelength region in which the phosphor plate 15 can be stimulated. Theflat radiator “PLANON” marketed by the Osram company can, for example,be used as such a second erasing lamp 12 of planar configuration.

[0021] The X-ray cassette 1 further contains a control means 13 with theaid of which the components contained in the X-ray cassette 1 aredriven. The control means 13 serves, in particular, to control the firsterasing lamp 11 and the second erasing lamp 12. The control means 13 isused to switch the two erasing lamps 11 and 12 into an on state, inwhich they output erasure radiation, and into an off state, in whichthey do not output erasure radiation. The second erasing lamp 12 isadvantageously switched into the on state by the control means 13immediately after the phosphor plate 15 has been erased by the firsterasing lamp 11. Thereafter, it continuously emits the erasure radiationof the weak, second intensity. The second intensity is advantageously soweak that its contribution to the total noise is negligible. The seconderasing lamp 12 is switched into the off state by the control means 13for the purpose of storing a new X-ray image in the phosphor plate 15.The new X-ray image can therefore be stored completely in the phosphorplate 15 without the second erasing lamp 12 already erasing even thetiniest portions of information. As already described above, the X-rayimage is subsequently read out with the aid of the reading head 10, andthe residual information, which continues to be stored in the phosphorplate 15 after the reading out, of the X-ray image is erased by means ofthe first erasing lamp 11.

[0022] It is likewise possible to leave the second erasing lamp 12 inthe on state even during storage of the new X-ray image. In this case,advantageously there need not be any tuning between the second erasinglamp and the radiation source which outputs the imaging radiation withthe information to be stored in the direction of the phosphor plate 15.The erasure radiation which can be output by the second erasing lamp 12can be fashioned such that there is no longer a need to switch off thesecond erasing lamp 12. It is therefore unnecessary for the sake ofsimplicity to incorporate and tune the functioning of the second erasinglamp 12 into the operation of imaging, reading out and erasing.

[0023]FIG. 2 shows a schematic sectional illustration of the phosphorplate 15 and of the second erasing lamp 12 in accordance with FIG. 1.The second erasing lamp 12 is arranged parallel to the phosphor plate 15inside the X-ray cassette 1. The second erasing lamp 12 emits, in thedirection of the phosphor plate 15, an erasure radiation 17 which hasthe weak, second intensity.

[0024]FIG. 3 shows a second exemplary embodiment of the X-ray cassette 1according to the invention. Instead of the second erasing lamp 12 fittedbelow the phosphor plate 15 (FIG. 1), a third erasing lamp 14 isarranged here at the rear lateral longitudinal wall of the X-raycassette 1. This third erasing lamp 14 is located laterally next to thephosphor plate 15 and extends along the longitudinal side thereof. Aplanar reflector 16 is arranged parallel to the phosphor plate 15 on theinside of the top cover of the X-ray cassette 1. The reflector 16 can bea mirror, for example.

[0025] The third erasing lamp 14 has the same function as the seconderasing lamp 12 of the first exemplary embodiment in accordance withFIG. 1. It emits erasure radiation of the weak, second intensity. Thisweak erasure radiation can be radiated partially by the third erasurelamp 14 directly onto the phosphor plate 15, or else can be directed bythe third erasing lamp 15 onto the reflector 16 and be reflectedthereby, in turn, in the direction of the phosphor plate 15. The erasureradiation output by the third erasing lamp 14 is distributed in this wayover the entire surface of the phosphor plate 15. The entire surface ofthe phosphor plate 15 is reached by the second erasure radiation 17because of the arrangements of the erasing lamp 14 and the reflector 16.

[0026]FIG. 4 shows a schematic sectional illustration of the X-raycassette 1 in accordance with the second exemplary embodiment of FIG. 3.The X-ray cassette 1 is illustrated here sectioned in the line directionB. The third erasing lamp 14 is arranged on the left-hand side of FIG.4. It is located in a fashion offset to the side of the reflector 16 andthe phosphor plate 15, at approximately the same distance from thereflector 16 and the phosphor plate 15, inside the X-ray cassette 1.

[0027]FIG. 5 shows an example of the-application of a third exemplaryembodiment of the X-ray cassette 1 according to the invention. In thisexample of application, the X-ray cassette 1 is inserted in an X-raytable 20. This X-ray table 20 includes an X-ray base 23 in which theX-ray cassette 1 is located, and a supporting surface 24 arranged onthis X-ray base 23. Patients are laid on this supporting surface 24 forX-rays to be taken. An X-ray source 21 is fitted on the X-ray table 20over the supporting surface 24 and the X-ray base 23 with the X-raycassette 1 located therein. The X-ray source 21 emits an X-ray radiation25 in the direction of the supporting surface 24 in order to take theX-ray image. The X-ray cassette 1 present in the X-ray base 23 herecontains a detection means 22 which serves as a sensor for the X-rayradiation 25. A sensor 22 can determine whether the X-ray source 21 isemitting X-ray radiation 25. The operability of the erasing meanscontained inside the X-ray cassette 1 can be controlled with the aid ofthe sensor 22.

[0028]FIG. 6 serves to illustrate further the functioning of the sensor22 and to describe the reading head 10. FIG. 6 shows the reading head 10and further components, present in the reading head 10, for reading outthe X-ray information stored in the phosphor plate 15. The reading head10 contains a laser diode row 34 extending along the line direction B.The laser diode row 34 serves for exciting a phosphor material 32 whichis applied to a transparent substrate material 33 and forms the phosphorplate 15 together with this substrate material 33. An exciting radiation38 output by the laser diode row 34 traverses the substrate material 33and penetrates into the phosphor material 32. The phosphor material 32emits an emission radiation because of this excitation of the phosphormaterial 32. This emission radiation is projected onto a CCD row 36 byan optical imaging means 35 which contains a multiplicity of opticalconductors, for example. The CCD row 36 includes a multiplicity oflight-sensitive surfaces 37 arranged in a row next to one another.

[0029]FIG. 6 further shows the sensor 22 for detecting X-ray radiation25. The sensor 22 contains a photodiode 30 over which a scintillationlayer 31 is arranged. The X-ray radiation 25 emitted by the X-ray source21 strikes this scintillation layer 31. The scintillation layer 31performs a wavelength conversion. The X-ray radiation 25 is convertedinto a radiation of a wavelength which can be detected by the photodiode30. The sensor 22 is connected to the control means 13. The informationemitted by the sensor 22 via the output of X-ray radiation 25 by theX-ray source 21 can be used by the control means 13 to drive the seconderasing lamp 12. In the exemplary embodiment in accordance with FIG. 6,this second erasing lamp 12 is arranged below the phosphor plate 15, asalready described in conjunction with FIG. 1.

[0030] If the second erasing lamp 12 is in its on state, such that itoutputs weak erasure radiation 17 in the direction of the phosphor plate15, the second erasing lamp 12 can then be switched into the off stateby the control means 13 when the sensor 22 establishes that the X-raysource 21 is emitting X-ray radiation 25 for the purpose of renewedstorage of an X-ray image in the phosphor plate 15. The second erasinglamp 12 can be switched off automatically in this way such that there isno erasure with the second erasure radiation 17 during the taking of anew X-ray image.

[0031] Instead of the photodiode 30 and the scintillation layer 31, thesensor 22 can also be configured otherwise. The configuration by meansof the photodiode 30 and the scintillation layer 31 constitutes avariant of the sensor 22 which is particularly easy to implement.

[0032] Two erasing lamps 11 and 12 or 14 are used in the previouslydescribed exemplary embodiments for the purpose of erasing the phosphorplate 15 by means of the strong and the weak erasure radiation. Insteadof two erasing lamps, it is likewise possible to make use of a singleerasing lamp, or else also of more than two erasing lamps. In the caseof a single erasing lamp, the latter is configured in such a way that itoutputs both the weak and the strong erasure radiation.

We claim:
 1. Device for reading out information stored in a storagelayer (15), having an erasing means (11, 12, 14) for erasing informationstored in the storage layer (15) by means of an erasure radiation (17),characterized in that the erasing means (11, 12, 14) is configured insuch a way that the erasure radiation (17) which can be output can adopta first and a second intensity, and the first intensity is larger thanthe second intensity.
 2. Device according to claim 1, characterized inthat the erasing means (11, 12, 14) is configured in such a way that itoutputs the erasure radiation (17) of the first intensity essentiallyimmediately after information of a first image has been read out. 3.Device according to claim 1 or 2, characterized in that the erasingmeans (11, 12, 14) is configured in such a way that it outputs theerasure radiation (17) of the second intensity after the erasureradiation (17) of the first intensity has been output.
 4. Deviceaccording to one of claims 1 to 3, characterized in that the erasingmeans (11, 12, 14) is configured in such a way that it outputs theerasure radiation (17) onto the storage layer (15) at least between thereading out of the information of a first image stored in the storagelayer (15) and the subsequent storage of information of a second imagein the storage layer (15).
 5. Device according to one of claims 1 to 4,characterized in that it has a control means (13) for driving theerasing means (11, 12, 14) such that the latter can be switched into anon state in which the erasure radiation (17) is output onto the storagelayer (15) and into an off state in which no erasure radiation (17) isoutput onto the storage layer (15).
 6. Device according to one of thepreceding claims, characterized in that the erasing means (11, 12, 14)is configured in such a way that erasure radiation (17) of the secondintensity can be output onto the storage layer (15) in operation duringthe storage of information in the storage layer (15).
 7. Deviceaccording to one of the preceding claims, characterized in that theerasing means (11, 12, 14) has a first erasing source (11) foroutputting the erasure radiation of the first intensity, and a seconderasing source (12, 14) for outputting the erasure radiation (17) of thesecond intensity.
 8. Device according to one of the preceding claims,characterized in that the erasing means (11, 12, 14) has an erasingsource (12) of planar configuration whose surface is arranged parallelto the storage layer (15).
 9. Device according to claim 7 and claim 8,characterized in that the second erasing source (12) is the erasingsource (12) of planar configuration.
 10. Device according to claim 8 orclaim 9, characterized in that the surface for outputting the erasureradiation (17) has at least the magnitude of the storage layer (15). 11.Device according to one of claims 1 to 7, characterized in that theerasing means (11, 12, 14) has an erasing source (14) which is arrangedlaterally next to the storage layer (15).
 12. Device according to claim11, characterized in that it has a reflector (16) for reflecting theerasure radiation (17) generated by the laterally arranged erasingsource, and the reflector (16) is arranged such that erasure radiation(17) reflected by it is directed onto the storage layer (15) duringoperation.
 13. Device according to one of the preceding claims,characterized in that it has a detection means (22) for detecting astorage radiation (25) which serves for storing the information in thestorage layer (15).
 14. Device according to claim 5 and claim 13,characterized in that the detection means (22) is connected to thecontrol means (13).
 15. Device according to claim 13 or claim 14,characterized in that the detection means (22) has a photodiode (30) anda conversion layer (31) for converting the storage radiation (25) into aradiation which can be detected by the photodiode (30).
 16. X-raycassette having a storage layer (15) for storing information, and adevice according to one of the preceding claims.
 17. Method for readingout information stored in a storage layer (15), information stored inthe storage layer (15) being erased by means of an erasure radiation(17), characterized in that the erasure radiation adopts a first and asecond intensity, and the first intensity is larger than the secondintensity.